As the hardest substance in nature, diamond has a lot of industrial applications, such as fine polishing materials, high hardness cutting tools, all sorts of augers, drawing dies, and parts for many precision instruments. However, there are rarely any high quality, large size (>1 mm) diamonds found in nature and they are very expensive. Therefore, there is a need to manufacture diamonds of large size.
In the currently available techniques, Chemical Vapor Deposition (CVD) can be applied to artificially produce diamonds. Using this method, the carbon containing gases (such as methane (CH4)) and hydrogen (H2) are first mixed at a certain ratio, and then excited by passing through RF plasma, direct current arc, microwave plasma, hot filament, or combustion flame. The mixed gases react on high temperature endurable substrate on which the small size single crystalline diamonds are pre-positioned. The small size single crystalline diamonds grow gradually to form thin film coating or thick polycrystalline coating with the same spatial structure as the diamond atoms, which are then separated from the substrate to form self-supported polycrystalline diamonds.
There are following issues with existing techniques. For example, utilization rate of the reaction zones is low. Currently available microwave plasma technique only allows the diamonds to grow in one cross section and in one dimension, which actually can grow inside the entire plasma sphere. In addition, the produced diamonds need to be cut after the production process, which increases the production cost and deceases the production efficiency. Method disclosed in U.S. Pat. No. 5,015,528 is directed to grow diamonds under the hydrogen atmosphere using fluidized bed, which allows the diamond growth larger than 0.1 mm. However, it is very difficult to grow larger diamonds using this method since the larger the particles, the higher flow is needed in the fluidized bed. The higher flow would destroy the conditions that are suitable for diamonds to grow. Industrial method such as microwave plasma requires low pressure or vacuum to make the atmosphere suitable for diamonds to grow where the seeds would be difficult to float. The methods provided in this invention can be applied to make the small size seeds grow larger by keeping the seeds continuously and repeatly in moving state when passing the reaction zones that are suitable for diamonds to grow.